The present invention relates to spray head devices and more particularly to a spray head device used in association with sewage disposal systems. In the past, floating plate spray heads, such as the spray head illustrated in U.S. Pat. No. 3,198,283 to Moore, have gained acceptance in a number of applications. Such spray heads are advantageous because they are of simple construction; they tend to be self-cleaning, and they include an orifice which expands and contracts in response to changes in pressure within the system. Because the orifice can change size, the flow rate through floating plate spray heads is a linear function of the system pressure whereas in fixed orifice nozzles the flow rate is a function of the square of system pressure. Floating back plate spray heads may thus accommodate increased liquid flow without an exponential increase in system pressure. Also, a floating plate spray head produces a spray pattern annulus which does not vary greatly with changes in liquid flow.
The shape and width of the annulus created by floating plate spray heads have not been highly satisfactory, however, due to the shape of the back plates which have been used in the past. The flow pattern created by a flat back plate such as shown in FIGS. 1 thru 4 of the Moore patent is umbrella shaped with liquid falling in a narrow ring. When tabs are added to the back plate as shown in Moore FIGS. 5 thru 8, the water falls from the nozzle in narrow spider-like streams which are spaced in a circular pattern about the nozzle.
Floating plate spray heads are also inherently disadvantageous because the back plates of such spray heads are biased downwardly by gravitational attraction only, so that downward force on the back plate changes imperceptibly as the back plate rises. When several of such nozzles are connected in parallel to a single source of pressurized liquid, some of the nozzle back plates rise fully while others do not rise at all unless the system is operating at relatively high pressures.